A difficult obstacle associated with the exploration and production of oil and gas is management of significant ocean currents. These currents can produce vortex-induced vibration (VIV) and/or large deflections of tubulars associated with drilling and production. VIV can cause substantial fatigue damage to the tubular or cause suspension of drilling due to increased deflections. Deflections of both production and drilling tubulars can be alleviated using various types of VIV suppression devices that can be attached to the tubular, for example, fairings, tail fairings, strakes, or other suppression systems.
Fairings may have a substantially triangular or tear drop shape, and work by streamlining the current flow past the tubular and thereby reduce the intensity of vortex shedding. With weaker vortices, both VIV and drag or deflection of the underlying tubular can be decreased.
Fairings may be constrained axially by collars. These collars are clamped tight around the tubular so that the fairings may be free to rotate with changes in current direction and restricted from sliding axially past the collar. Various arrangements of collars and fairings are possible.
An issue associated with drilling riser fairings is that they can be time consuming to install. Of the installation time, usually well over half is due to the time it takes to install the collars. While it would be beneficial to be able to install the collars quickly, it would also be beneficial to be able to pre-install the collars in the yard or in storage rather than install them during installation of the riser. These needs are also true of collars used on production tubulars, which can have insulation, buoyancy or other thick coatings.
Buoyancy is often required for drilling risers, especially those operating in deeper waters. Buoyancy reduces the amount of weight that the vessel has to support so that lighter and smaller vessels can drill effectively. Buoyancy also influences the dynamics of the entire drill string including the wellhead.
Insulation is often required for production tubulars in order to keep the production fluids at a temperature that optimizes production. Like buoyancy, insulation is typically preinstalled on the tubular and can have a range of thicknesses.
Some tubulars, especially drilling risers, can have auxiliary lines external to the main tubular. The lines can potentially impede the rotation of the fairing that covers the main tubular and the auxiliary lines. In addition, the lines must pass over or through the collars as they travel axially along the main tubular.